In multi-cellular organisms the interactions between extracellular and intracellular compartments play an important role in controlling many developmental decisions. In animal cells there has been solid evidence that extracellular matrix (ECM) molecules are constituents of selective cell-cell recognition and cell-ECM adhesion processes and are important in regulation of developmental processes such as cellular polarity, differentiation, cell division, cell death and cell migration. This proposal concerns a family of five ECM-associated receptor-like protein kinases, Waks (Wall Associated Kinase), which appear to be adhesion receptors that exchange signals between the extracellular and intracellular compartments of Arabidopsis. Waks have a transmembrane domain that separates an amino-terminal, extracytoplasmic domain that have EGF (Epidermal Growth Factor) repeats and limited sequence identities to either the tenascin superfamily, or the neurexins. The carboxyl region of all the Waks encode a cytoplasmic serine/threonine protein kinase. Waks are localized in the plasma membrane. Moreover, the Wak1 kinase domain interacts with a cytoplasmic type 2C protein phosphatase. Both an insertional mutation and a dominant negative mutation of Wak1 have been isolated and found to be lethal, indicating that the protein is essential. This proposal describes experiments to dissect the signaling pathways associated with Waks and to determine the role Waks have in signal transduction between the plant ECM and the cytoplasm. The analysis of the Wak family of proteins may lead to a description of a new signal transduction mechanism in plant cells, and perhaps toward general principals of how eukaryotic cells perceive architectural changes in their extracellular matrix and environment.